Organic phosphites are well-known and are commonly used as secondary antioxidants in polymer compositions including, for example, polyolefins, polyvinyl chloride, and elastomers. Examples of such phosphites are disclosed in H. Zweifel (Ed) Plastics Additives Handbook, 5th edition, Hanser Publishers, Munich 2000. Phosphite stabilizers, both liquid and solid, are known in the art.
Many of the most effective organic phosphites are solids at ambient temperature and accordingly do not lend themselves to being processed with certain polymers. Owing to their solid form and concomitant processing limitations, for example, some solid alkylaryl phosphites have been demonstrated to plateout during processing in some plastics, in particular low melting point plastics, and form deposits on processing machinery surfaces. In addition, solid organic phosphites typically must be processed, e.g., heated and melted, in order to be incorporated into the respective polymer compositions thereby increasing handling and processing costs.
One of the most widely used solid organic phosphites is tris(2,4-di-t-butylphenyl) phosphite, which is commercially sold under the trade name Alkanox™ 240 (Chemtura Corporation, Middlebury, Conn., USA), Irgafos™ 168 (Ciba Specialty Chemicals Corporation, Tarrytown, N.Y., USA), or Doverphos™ S-480 (Dover Chemical Corp, Dover, Ohio, USA). Tris(2,4-di-t-butylphenyl)phosphite has processability and solubility limitations, however, due to its solid form.
Liquid phosphite compositions are also well known and do not possess the handling problems associated with solid phosphite compounds. In addition, liquid phosphite compositions generally exhibit better processability than solid phosphite compositions for polymers that process at low temperatures. Tris(p-nonylphenyl)phosphite (TNPP), for example, is one alkylaryl phosphite that is a stable liquid at ambient conditions.
TNPP is a versatile phosphite stabilizer that is useful in stabilizing a large number of polymers such as HDPE, LLDPE, SBR, ABS, PVC and others.
Most commercially available alkylaryl phosphites are derived from phenols. U.S. Pat. No. 5,254,709, for example, the entirety of which is incorporated herein by reference, describes the synthesis of tris(2,4-di-tert-butyl)phenyl phosphite by reacting an alkylated phenol intermediate, i.e., 2,4-di-tert-butyl phenol, with phosphorus trichloride in the presence of catalyst according to the following reaction:

Generally, phosphites derived from phenols may include some residual phenols, which may present health and/or environmental issues. Para-nonylphenol, for example, which is used in synthesizing TNPP, has alleged estrogenic effects. Thus, the need exists for novel alkylaryl phosphites and for methods for making such alkylaryl phosphites. Several non-phenol sources have been proposed to make phosphites in the following patent literature.
GB Patent No. 2,227,490 describes reacting a 2-methyl-6-t-butyl-phenol, e.g., a 6-t-butyl-ortho-cresol, and biphenyl with a phosphorous trichloride to form a composition of: 0-5 mol % of 2-methyl-6-t-butyl-phenol; 35-45 mol % of tris(2-methyl-6-t-butyl-phenyl)phosphite; 10-20 mol % of bis(2-methyl-6-t-butyl-phenyl)biphenyl phosphonite; 30-40 mol % of bis(2-methyl-6-t-butyl-phenyl)biphenyl diphosphonite. The individual phosphites and phosphonites are separated and used as secondary antioxidants.
U.S. Pat. No. 3,558,554 describes various individual phosphites including di-n-butyl(2-t-butyl-p-cresyl)phosphite, di-n-hexyl(2-t-butyl-m-cresyl)phosphite, di-n-hexyl(2-t-butyl-p-cresyl)phosphite, di-n-octyl(2-t-butyl-p-cresyl)phosphite, di-n-butyl(2,6-di-t-butyl-p-cresyl)phosphite, di-phenyl(2-t-butyl-p-cresyl)phosphite, tri(2-t-butyl-p-cresyl)phosphite, di(ethylthioethyl)(2-t-butyl-p-cresyl)phosphite, and di(octylthioethyl)(2-t-butyl-p-cresyl)phosphite.
U.S. Pat. No. 4,261,880 describes tricresylphosphite.
U.S. Pat. No. 4,383,950 describes various individual phosphites including tris(di-2-t-octyl-4-methylphenyl)phosphite, tris(di-2-t-octyl-4-t-butyl-5-methylphenyl)phosphite, and tris(di-2-t-butyl-4-t-octyl-5-methylphenyl)phosphite.
U.S. Pat. No. 4,406,842 describes a O,O′-bis(2-t-octyl-4-methylphenyl)phenyl phosphite as a secondary stabilizer.
U.S. Pat. No. 5,322,871 describes bis(2,4-di-alkyl-o-cresyl)phosphite derivatives, including bis(2,4-di-t-butyl-6-methylphenyl)4-nonylphenyl phosphite and bis(2,4-di-t-butyl-6-methylphenyl)4-t-butyl-phenyl phosphite as secondary antioxidants.
U.S. Pat. No. 6,887,926 describes secondary stabilizers including: bis(2,6-di-t-butyl-4-methylphenyl)pentarythritol diphosphite, bis(2,4-di-t-butyl-6-methylphenyl)pentarythritol diphosphite, bis(2,4-di-t-butyl-6-methylphenyl)methyl phosphite and bis(2,4-di-t-butyl-6-methylphenyl)ethyl phosphite.
Notwithstanding the above literature, the need remains for safe and effective phosphite stabilizers for polymers against heat and light degradation and that are liquid at ambient conditions.